Jessica Bewley stored her grandfather's letters and other family heirlooms in her locker.

The Wellingtonian now lives in Sydney and learned about the blaze from a friend who sent her photos this morning.

"I've now notified my parents who now live abroad also and we are just waiting now to hear anything," she said.

Bewley was gutted about the possibility her inherited letters were gone, she said.

"I guess though at the end of the day it is only material possessions that have been lost."

HUGE OPERATION

About half of the 20 fire trucks brought in overnight have now been sent home.

In a statement, Fire Service assistant area commander Paul Smith said the fire was not endangering any other buildings. Part of the difficulty was that the building was made up of numerous locked compartments.

The initial responding crew had gained access, but were forced back, as the building had upright concrete slabs at both ends and one was threatening to collapse.

Smith told Fairfax Media that by 9am firefighters still had not been able to re-enter the 25m-by-80m building because it was "too dangerous".

There were no signs anyone was in the building but fire fighters would be checking on this when they got inside.

A digger has now removed a large corner of the building and fire fighters are spraying foam in to quell the remaining flames.

At the peak of the Fire Service's response, up to 100 crew battled the blaze, with all on-duty Wellington crew called in, as well as some from Porirua and Hutt Valley.

One firefighter suffered mild heat stress and is now resting at home.

Thick smoke from the fire will continue for some time and residents and workers in the area were advised to close their windows or leave the area if they can.

Pollution control officers were coming to assess what was in the smoke and an environmental response team was on the way to consider whether it was necessary to evacuate residents.

Smith was not sure whether there were any hazardous substances in the building, however he believed the building would have regulation about storing hazardous goods.

Smith said the fire was not the biggest he had seen in Wellington "but it's up there".

Earlier attempts to pull roofing iron off failed because of the intense heat.

He estimated the interior of the warehouse to be between 800degC to 1000degC.

HEALTH CONCERNS

Regional Public Health medical officer of health Stephen Palmer said the smoke would only be tested for toxins if toxic material was found inside.

Smoke would contain particles, gas, and water vapour.

Any toxins were likely in small amounts. Smoke could irritate eyes, nose, throat and airways.

It could cause runny or sore eyes, sore throat, sore nose, a cough, or chest tightness.

For most healthy people the symptoms would disappear when exposure ended.

But smokers, elderly, young children, or those with health problems could be at more risk and should get medical help if required.

TRANSPORT AFFECTED

Due to the fire in Kilbirnie, our buses can't get through the cordoned area - some school service disruptions advised http://t.co/VAAi9kaHpJ